Selective Oxidative Coupling of Methane to Ethylene in a Solid Oxide Electrolyser Based on Porous Single‐Crystalline CeO₂ Monoliths

Catalytic conversion of CH 4 to C 2 H 4 plays an important role in the light olefin industry. Here, we report the electrochemical conversion of CH 4 to C 2 H 4 /C 2 H 6 at the anode with the electrolysis of CO 2 to CO at the cathode in a solid oxide electrolyser. We constructed well‐defined interfaces that function as three‐phase boundaries by exsolving single‐crystalline Ni nanoparticles in porous single‐crystalline CeO 2 monoliths. We engineered the chemical states and flux of active oxygen species for the oxidation of CH 4 at the anode by controlling voltage and temperature. We show the unprecedented C 2 selectivity (C 2 H 4 and C 2 H 6 ) of ≥99.5 % at a CH 4 conversion of ≈7 %. The electrolyser exhibits excellent durability without performance degradation being observed in a continuous operation of 100 hours. Our work enables a novel path for the selective conversion of CH 4 /CO 2 into useful chemicals, and the technique of building well‐defined interfaces may find potential applications in other fields.